1. Field of the Invention
The invention relates to a measurement bridge that is created on a printed circuit board and that can be used for example but not limiting within a network analyzer for forwarding the excitation signal to a reference port and a central output port having a device under test connected thereto and for forwarding a reflected signal from the device under test to a measurement port.
2. Discussion of the Background
An excitation signal is generated by a network analyzer for analyzing a device under test (DUT). The excitation signal is fed to said device under test via ports thereof. For example, in order to determine an input reflection coefficient and a forward transmission coefficient, an output reflection coefficient and a reverse transmission coefficient, the excitation signal is fed to the device under test, which comprises an input gate and an output gate, via said input gate or said output gate. In order to determine the reflection coefficients and the transmission coefficients, the respective incident and the returning waves of the excitation signal at the input gate and/or the output gate of the test object are to be determined. In order to determine the frequency range at which the excitation signal passes through the test object, and the frequency range at which the excitation signal is reflected at the input gate and/or the output gate of the test object, the network analyzer drives the frequency of the excitation signal through a predetermined frequency range in a frequency sweep.
A network analyzer of this type is known, for example, from US 2008/290880 A1. This publication shows a measurement bridge that can be used within a network analyzer. A reference signal corresponding to the excitation signal can be extracted from a reference channel and a measuring signal corresponding to a signal reflected from the measuring object can be extracted from a measuring channel. The measuring bridge comprises a resistive bridge and at least one hybrid coupler which is connected to the resistive bridge in series. The measurement bridge is operated as a resistive bridge in low frequency range and as a hybrid coupler in an upper frequency range.
It is a drawback of the confirmation of US 2008/290880 A1 that the measurement bridge comprises a resistive bridge and at least one hybrid coupler which are used for different frequencies. Thus, further circuit elements like a selecting unit or a relay-switch are needed to feed a signal either from the resistive bridge or from the at least one hybrid coupler to the Analog/Digital-converter. The use of the plurality of the hybrid couplers as well as of the resistive bridge and the switching unit leads to additional calibration routines and also reduces the sensitivity of the network analyzer.